This invention relates to video signals and, more particularly, to apparatus and method for encoding and decoding video signals for use in high definition television systems as well as in other applications including storage and/or transmission, over any suitable medium, of moving images in a form that requires reduced storage capacity and/or reduced bandwidth channels. The techniques hereof can be employed, for example, in so-called "compatible" high definition television approaches that use a separate auxiliary or "augmentation" channel to send picture detail information that augments conventionally received television information to obtain high definition performance, as well as in so-called "simulcast" approaches wherein a complete and independent high definition television signal is sent, on a separate channel, simultaneously with a conventional transmission of the same program information. Some of the techniques hereof can also be employed in so-called "enhanced definition" approaches that send picture enhancement information (but less than the information needed for full high definition performance) on the same channel with a conventional television program.
As high definition television (HDTV) becomes more prevalent, improved systems are needed for transmission and reception of the additional information required for presenting HDTV images. Any new service which provides higher definition television than is conventionally broadcast (i.e., more elements per line and lines per frame, and thus a wider bandwidth necessary for transmission) should serve existing home television receivers with essentially all the picture attributes and quality of which the receivers are capable. Also, receivers designed for new (high definition) service, should be capable of operating using the pre-existing transmissions and derive from them a result not inferior to that provided by pre-existing receivers.
A variety of HDTV schemes have been proposed. In U.S. Pat. Nos. 4,517,597, 4,628,344, 4,652,909, 4,701,783, and 4,800,426, assigned to the same assignee as the present application, as well as in the publication "HDTV Compatible Transmission System", W. E. Glenn, National Association of Broadcasters, April, 1986, there is disclosed an HDTV system that utilizes an augmentation approach which permits compatible transmission of HDTV. The disclosed techniques also have application to video bandwidth compression and to reducing video storage capacity.
As described in the referenced patents and publication, an electronic video signal (e.g. a television signal) can be encoded at reduced bandwidth by lowering the frame refresh rate of the high spatial frequency components, while maintaining the frame refresh rate of at least a portion of the low spatial frequency components at the standard rate. If done in a specified manner this will not cause substantial degradation in the ultimately displayed image, since human vision cannot perceive changes in high spatial resolution information at as fast a rate as it can perceive changes in low spatial resolution information. Accordingly, as has been previously set forth, an electronic video encoding and decoding system can be devised which takes advantage of this, and other, characteristics of human vision by encoding higher spatial resolution video components to be at a temporal information rate which approximately corresponds to the highest rate actually perceived by human vision for such components; thereby eliminating the need to encode these components at a higher rate, which inherently wastes bandwidth. Also, as shown in referenced patent and publication, the low spatial resolution information can be generated in a form which is compatible with standard television video, for example NTSC video used in the U.S. It has also been recognized that a number of frequency components can be transmitted at specified rates [see e.g. W. F. Schreiber et al., Reliable EDTV/HDTV Transmission In Low Quality Analog Channels, SMPTE Journal, July 1989, and the abovereferenced patents of the present assignee], with components selected according to degree of motion in order to have higher spatial resolution in scenes with little motion and higher temporal resolution in scenes with a great deal of motion.
FIG. 1 illustrates a compatible high definition television transmission and receiving system of the general type described in the above-referenced patents and publication. A transmitter 200 includes NTSC processing circuitry 210 which processes television signals from a source such as a television camera system (not shown) or a video recording system (not shown). The circuitry 210 is coupled to transmitting circuitry 215, which typically includes modulation circuitry and other suitable circuitry for producing a signal to be transmitted over a standard NTSC channel. The television signals from the television camera system or video recorder (which is assumed to have a high definition video capability) are also processed by high definition television (HDTV) processing circuitry 260 which produces detail signals that can be utilized to enhance conventional television signals to obtain HDTV signals, as described in the abovereferenced patents and publication. [As further described in the referenced U.S. Pat. No. 4,652,909, the detail signal can be obtained from a separate camera.] The detail signals are coupled to further circuitry 275, which transmits the detail signal over a second (auxiliary) channel that is typically not adjacent to the (main) NTSC channel used for transmission of the standard portion of the television information. The NTSC signal is received by receivers such as receiver 310 which has only a capability of producing a television picture at substantially conventional resolution e.g. conventional display 315. Receivers such as receiver 360, which have a capability for receiving, processing, and displaying high definition television signals, receive both the main channel carrying the NTSC signal and the auxiliary channel carrying the detail signals to be used for augmentation of the NTSC video signal so as to produce a high definition television signal for display on an HDTV display 365.
In the referenced patents and publication, the spatial detail is transmitted at a relatively slow frame rate, such as 15 or 7.5 frames per second. "Jutter" (jerky edge motion) was observed when the detail frame rate was reduced too far. This artifact constrains the augmentation channel bandwidth to be larger than would otherwise be indicated by psychophysical studies. Camera lag, caused by the integration of image energy on the face of the camera tube, which attenuates detail in moving areas of the picture, can be exploited to reduce jutter, but some reduction in image detail can be observed in moving objects when they are visually tracked.
It is among the objects of the present invention to provide improvements in performance and in bandwidth compression with respect to the techniques described above and with respect to other prior art techniques. It is also among the objects hereof to provide such improvements in a system that can be made compatible with existing or future television standards (for example, NTSC, or other standards such as PAL or SECAM).
As further background to the invention, reference can be made to the following U.S. Patents which relate to compression, transmission and/or other processing of video signals and/or still picture information:
U.S. Pat. Nos. 4,196,448, 4,210,931, 4,224,678, 4,302,775, 4,394,774, 4,541,012, 4,605,952, 4,630,099, 4,661,862, 4,672,425, 4,675,733, 4,675,750, 4,729,012, 4,774,562, 4,780,761, 4,791,598, 4,807,029, 4,821,119, 4,845,562, 4,851,906, 4,870,489, 4,873,573.